Enhance GT.fmt_image() to support http/https schema in the columns parameter

[jrycw]

Related PRs: #444, #451.

Currently, GT.fmt_image() supports formatting images from URLs by combining the columns and path parameters, as shown below:

import polars as pl
from great_tables import GT, vals, html

img_path = "https://raw.githubusercontent.com/posit-dev/great-tables/refs/heads/main/great_tables/data/metro_images/"

df = pl.DataFrame({"lines": ["tram_T6.svg", "tram_T7.svg", "tram_T8.svg"]})
GT(df).fmt_image("lines", path=img_path)

---

This PR proposes an enhancement to allow image formatting using only the columns parameter, enabling the following code to execute without errors:

df2 = df.with_columns(pl.lit(img_path).add(pl.col("lines")).alias("lines"))

GT(df2).fmt_image("lines")  # It produces the same table as the original approach.

This modification should benefit users who retrieve a list of URLs through a database query and store them as a column in the DataFrame. A possible scenario can be illustrated with the following pseudo-code:

...
urls: list[str] = db.execute("SELECT url FROM Foo")
df = pl.DataFrame({"urls": urls})
GT(df).fmt_image("urls")

---

Additionally, this change would make it more convenient for users who want to place images in locations other than the body using vals.fmt_image(). For example:

header_imgs = vals.fmt_image(f"{img_path}tram_T5.svg")
GT(df2).fmt_image("lines").tab_header(title=html(header_imgs[0]))

---

I believe this improvement will enhance the user experience and better align with the documentation, which states that complete http/https URLs should be accepted. That said, I'm open to any suggestions or feedback!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.72%. Comparing base (4771178) to head (f76e2cb).
Report is 49 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #520   +/-   ##
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  Coverage   89.71%   89.72%           
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  Files          45       45           
  Lines        5202     5206    +4     
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+ Hits         4667     4671    +4     
  Misses        535      535           

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[jrycw]

By the way, the new ruff settings appear to be working smoothly, and it seems our project runs on Python 3.13 without any issues.

[machow]

This LGTM, @rich-iannone do you want to merge?